The ultimate objective of the proposed research is to identify the proteins in the inner membrane of the mitochondrion which interact with the F1-ATP'ase and confer reversibility to it. To achieve this goal the determination of the complete amino acid sequence of the five constituent polypeptide chains of the F1-ATP'ase has been initiated. The elucidation of the amino acid sequence of the individual subunits of the F1-ATP'ase will provide guidelines to study the interactions between the F1-ATP'ase and other membrane proteins by cross-linking studies. derivatives containing photoactivatable groups will be attached to surface residues on the individual subunits of the F1-ATP'ase. The modified F1-ATP'ase will be added to depleted membrane preparations which confer reversibility to it and the recombined complexes will be illuminated to cross-link the ATP'ase subunits to protein neighbors in the membrane. Comparison of the behavior of the cross-linked preparations and suitable controls by polyacrylamide gel electrophoresis in the prescence of sodium dodecyl sulfate will be the method by which the specificity of cross-linking will be monitored.